Damage-tolerant coating

ABSTRACT

A coating composition having excellent damage tolerance. The coating composition includes a binder system comprising at least a fluoropolymer, optionally, one or more other resin components, a crosslinking component and at least one inorganic filler and organic filler. Coated articles with the coating composition applied to at least a portion of a surface thereof are also provide.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This international application claims benefit from U.S. ProvisionalApplication No. 62/281,059 filed 26 Jan. 2016 and entitled“Damage-Tolerant Coating,” which is incorporated herein by reference inits entirety.

BACKGROUND

Polymer coating compositions are routinely applied to substrates,especially metal substrates. Such coatings are used for a variety ofreasons, including, for example, to protect the substrate fromdegradation, to beautify the substrate (e.g., to provide color,brightness, etc.), and the like.

Many such polymer coating compositions are applied on planar substrates(e.g., using coil coating processes) that are subsequently formed intofinished articles, including articles used as exterior buildingmaterials, for light fixtures, and the like. The coating must alsomaintain a suitable aesthetic appearance (color, smoothness, gloss, andthe like) over the various processes involved in bringing a coil-coatedproduct to the consumer, including forming, shipping, handling, andinstallation.

Coil-coated parts, including coatings made with fluoropolymers, areeasily damaged during handling and installation. To reduce such damage,manufacturers often place a laminate protecting sheet on coil-coatedpanels prior to shipping. However, this adds labor and materials coststo the process. Other conventional methods of preventing damage includeadding filler material to the coating composition, but this produces avisibly significant textured appearance and a displeasing tactilefeature that is not desired or acceptable for many coil coatingapplications, including coil coated panels used for building materialsor architectural surfaces.

Accordingly, there is a continuing need for coil coatings and coilcoated parts that demonstrate excellent damage tolerance with optimalsmoothness and desirable tactile feel.

SUMMARY

In one embodiment, the present description provides a coated articleincluding a substrate with a cured coating disposed thereon. The curedcoating is derived from a coating composition including a resincomponent including at least one fluoropolymer, an organic fillermaterial with particle size no more than 15 μm, and an inorganic fillermaterial with particle size no more than 15 μm. The coating has a smoothappearance and demonstrates increased damage tolerance relative to acoating derived from a conventional coating composition.

In another embodiment, the present description provides a coatingcomposition from which a coating disposed on at least of a portion ofsurface of a metal substrate is derived. The coating has increaseddamage tolerance relative to a coating derived from a conventionalcoating.

In yet another embodiment, the present description provides a method ofproducing a coated article from a metal substrate, wherein the substratehas, disposed on at least a portion of its surface, a cured coatingformed from the coating composition described herein.

Definitions

Unless otherwise specified, the following terms as used herein have themeanings provided below.

The term “crosslinker” refers to a molecule capable of forming acovalent linkage between polymers or between two different regions ofthe same polymer. The term “curing agent” is used interchangeably withthe term “crosslinker” herein.

The term “on”, when used in the context of a coating applied on asurface or substrate, includes both coatings applied directly orindirectly to the surface or substrate. Thus, for example, a coatingapplied to a primer layer overlying a substrate constitutes a coatingapplied on the substrate.

Unless otherwise indicated, the term “polymer” includes bothhomopolymers and copolymers (i.e., polymers of two or more differentmonomers). Similarly, unless otherwise indicated, the use of a termdesignating a polymer class such as, for example, “polyester” isintended to include both homopolymers and copolymers (e.g.,polyester-urethane polymers).

The term “comprises” and variations thereof do not have a limitingmeaning where these terms appear in the description and claims.

The terms “preferred” and “preferably” refer to embodiments of theinvention that may afford certain benefits, under certain circumstances.However, other embodiments may also be preferred, under the same orother circumstances. Furthermore, the recitation of one or morepreferred embodiments does not imply that other embodiments are notuseful, and is not intended to exclude other embodiments from the scopeof the invention.

As used herein, “a,” “an,” “the,” “at least one,” and “one or more” areused interchangeably. Thus, for example, a coating composition thatcomprises “an” additive can be interpreted to mean that the coatingcomposition includes “one or more” additives.

Also herein, the recitations of numerical ranges by endpoints includeall numbers subsumed within that range (e.g., 1 to 5 includes 1, 1.5, 2,2.75, 3, 3.80, 4, 5, etc.). Furthermore, disclosure of a range includesdisclosure of all subranges included within the broader range (e.g., 1to 5 discloses 1 to 4, 1.5 to 4.5, 1 to 2, etc.).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical representation of damage tolerance.

DETAILED DESCRIPTION

In one embodiment, the present description provides a cured coatingformed from a thermosetting coating composition that exhibits excellentdamage tolerance. The coating composition typically comprises a binderresin, an organic filler component, and an inorganic filler component.The binder system preferably includes at least a first resin component,and optionally, one or more additional resin components. Preferably, thecoating composition includes at least a film-forming amount of thebinder system. Although coating compositions including a liquid carrierare presently preferred, it is contemplated that the compositiondescribed herein may have utility in other coating applicationtechniques such as, for example, powder coating, extrusion, orlamination.

The binder system described herein includes at least a first resincomponent. The first resin component is preferably a halogenatedpolymer, more preferably a fluoropolymer. As used herein, the term“fluoropolymer” means a polymer or copolymer containing at least 50 molepercent fluoromonomer units. Suitable fluoromonomer units include, forexample, vinylidene fluoride, vinyl fluoride, trifluoroethylene,chlorotrifluoroethylene (CTFE), tetrafluoroethylene (TFE),hexafluoropropylene (HFP), and the like.

In an aspect, the fluoropolymer of the composition described herein ispoly(vinylidene fluoride) or PVDF, a homopolymer wherein at least 50 wt%, preferably 70 wt %, more preferably 90 wt % of fluoromonomer unitsare vinylidene fluoride.

In certain embodiments, the fluoropolymer described herein may be anacrylic-modified PVDF composition, i.e. PVDF modified with athermoplastic acrylic polymer, i.e. a copolymer of one more lower alkyl(C1-C6 alkyl) methacrylate esters and/or one or more lower alkylacrylate esters. In an aspect, the acrylic-modified PVDF describedherein preferably includes at least about 70%, more preferably 85 wt %PVDF and at least 5 wt % of the acrylic polymer. More preferably, theacrylic-modified PVDF includes about 85 to 95 wt % PVDF and about 5 to15 wt % of the thermoplastic acrylic polymer.

The fluoropolymers described herein preferably include PVDF havingweight average molecular weight (Mw) of about 150,000 to 500,000, morepreferably 350,000 to 450,000. The ratio of weight average molecularweight to number average molecular weight (Mw/Mn) is at least about 3.5,preferably about 3.5 to 50.0, and the fluoropolymer has a melting pointof preferably about 120° to 200° C., more preferably 150° to 170° C.Suitable fluoropolymers are commercially available, and include, forexample, the KYNAR line of polyvinylidene difluoride products (Arkema,Philadelphia Pa.).

In an embodiment, the binder system may optionally include one or moreother resin components in addition to the first resin component. Theseresin components may be identical to the first resin component, ordistinct from the first resin component. Suitable other resins include,for example, acrylic polymers or copolymers, polyesters, epoxies,silicone-modified polyesters, polyurethanes, and the like, and mixturesand combinations thereof.

The amount of the binder component in the coating composition describedherein is preferably about 1 to 65 wt %, more preferably about 15 to 50wt %, and most preferably about 20 to 40 wt %, based on the total weightof the coating composition. The amount of binder used in the compositionwill vary depending on the resin component(s) selected, and on desiredend uses for the coating.

In an embodiment, the coating composition further includes a crosslinkeror curing agent. The crosslinker may be used to facilitate cure of thecoating and to build desired physical properties. When present, theamount of crosslinker will vary depending upon a variety of factors,including, e.g., the intended end use and the type of crosslinker.Typically, one or more crosslinkers will be present in the coatingcomposition in an amount greater than about 0.01 wt-%, more preferablyfrom about 5 wt % to about 50 wt %, even more preferably from about 10wt % to about 30 wt %, and most from about 15 wt % to about 20 wt %,based on total weight of resin solids.

Polymers having hydroxyl groups are curable through the hydroxyl groups.Suitable hydroxyl-reactive crosslinking agents may include, for example,aminoplasts, which are typically oligomers that are the reactionproducts of aldehydes, particularly formaldehyde; amino- oramido-group-carrying substances exemplified by melamine, urea,dicyandiamide, benzoguanamine and glycoluril; blocked isocyanates, or acombination thereof.

Suitable curing agents also include aminoplasts, which are modified withalkanols having from one to four carbon atoms. It is suitable in manyinstances to employ precursors of aminoplasts such as hexamethylolmelamine, dimethylol urea, hexamethoxymethyl melamine, and theetherified forms of the others. Thus, a wide variety of commerciallyavailable aminoplasts and their precursors can be used. Suitablecommercial amino crosslinking agents include those sold by Cytek underthe tradename CYMEL (e.g., CYMEL 301, CYMEL 303, and CYMEL 385 alkylatedmelamine-formaldehyde resins, or mixtures of such resins, are useful) orby Solutia under the tradename RESIMENE.

Suitable crosslinkers may also include blocked isocyanates, such as, forexample, as described in U.S. Pat. No. 5,246,557. Blocked isocyanatesare isocyanates in which the isocyanate groups have reacted with aprotecting or blocking agent to form a derivative that will dissociateon heating to remove the protecting or blocking agent and release thereactive isocyanate group. Some examples of suitable blocking agents forpolyisocyanates include aliphatic, cycloaliphatic or aralkyl monohydricalcohols, hydroxylamines and ketoximes. Presently preferred blockedpolyisocyanates dissociate at temperatures of around 160° C. Thepresence of a catalyst is preferred to increase the rate of reactionbetween the liberated polyisocyanate and the active hydrogen-containingcompound (e.g., a hydroxyl-functional polyester). The catalyst can beany suitable catalyst such as, for example, dibutyl tin dilaurate ortriethylene diamine.

Suitable crosslinkers also include unblocked isocyanates. Unblockedisocyanates are difunctional or polyfunctional isocyanates with freeisocyanate groups attached to aliphatic, cycloaliphatic, aryl,araliphatic and/or aromatic moieties. Examples include, withoutlimitation, tetramethylene diisocyanate, hexamethylene diisocyanate,dodecamethylene diisocyanate, 1,4-diisocyanatocyclohexane,3,5,5-trimethylcyclohexyl isocyanate, isophorone diisocyanate, and thelike.

In some embodiments, an ultraviolet curing crosslinker or anelectron-beam curing crosslinker may be suitable. Examples of suitablesuch crosslinkers may include 1,6-hexanediol diacrylate, 1,4-butanedioldiacrylate, trimethylolpropane triacrylate, or mixtures thereof.

The coating composition described herein may be produced by conventionalmethods known to those of skill in the art. In an embodiment, thecoating composition is prepared by use of a polymerization or processingaid, such as a catalyst, for example. Suitable processing aids include,without limitation, metal catalysts (e.g., stannous oxalate, stannouschloride, butylstannoic acid, dibutyl tin oxide, tetrabutyltitanate, ortetra butylzirconate), antioxidants (e.g., hydroquinone,monotertiarybutyl-hydroquinone, benzoquinone,1,4-napthoquinone,2,5-diphenyl-p-benzoquinone, or p-tertbutylpyrocatechol), unblocked and blocked acid catalysts (e.g.,dinonylnaphthalene sulfonic acid, dinonylnaphthalene disulfonic acid,dodecyl benzene sulfonic acid, p-toluene sulfonic acid, phosphateesters, and mixtures or combinations thereof), and mixtures thereof. Theamount of catalyst depends on the amount and nature of the reactants,but is up to about 5 wt %, preferably up to about 2 wt %, based on thetotal weight of resin solids.

Other additives known in the art may be included in the coatingcomposition described herein. These additives include, withoutlimitation, flatting agents, fillers, flow or viscosity modifiers,texture-providing additives, waxes and/or other binders that may beincluded or dispersed in the coating composition. These additives aretypically included in the coating composition to provide or enhanceparticular properties of the cured coating formed from the composition.

In an embodiment, the coating described herein demonstrates excellentdamage tolerance when used as a coil coating, for example.Conventionally, coil coatings made from fluoropolymers like PVDF, forexample, are easily damaged during shipping, handling and installation.It is common practice in the industry to provide a protective laminatesheet on coated articles or panels prior to shipment. However, this addstime, labor and significant material costs to the process of transportand shipment of coated panels or articles.

One solution to the problem of coating damage during shipping, handlingand installation has been to include filler particles, such aspolytetrafluoroethylene (PTFE) particles, in the composition. However,the PTFE particles tend to produce a significantly textured or roughappearance, and in some applications such as standing wall buildingpanels, for example, the inclusion of PTFE in the composition provides acoating with a displeasing or undesirable tactile feel.

Surprisingly, the composition described herein provides a cured coatingthat demonstrates excellent damage resistance while maintaining a smoothsurface and an appealing or desirable tactile feel. The cured coatingdemonstrates increased damage tolerance relative to coatings derivedfrom conventional coating compositions, including conventional coilcoating compositions, for example. Without limiting to theory, theexcellent damage resistance is believed to be the result of fillerparticles that reduce friction between coating layers on adjacent coatedsheets or articles in a way that minimizes damage.

In an embodiment, the coating composition described herein includes atleast one organic filler and at least one inorganic filler. Suitableorganic fillers include, without limitation, polymeric fillers, waxes,viscosity modifiers, and the like, and mixtures or combinations thereof.In a preferred aspect, the organic filler is a polymeric filler.Examples of suitable polymeric fillers include, without limitation,polyvinyl acetate, vinyl acetate copolymers, polystyrene, polyethylene,polytetrafluoroethylene (PTFE), polypropylene, polybutylene,polybutadiene, copolymers of butadiene and styrene, polyacrylonitrile,polyacrylate esters, silyl-modified polymethacrylate esters, and thelike, and mixtures or combinations thereof. In some embodiments, theorganic filler may be a high melting, high molecular weight polyolefinmaterial. In a preferred aspect, the polymer filler material is PTFE.

The polymeric filler described herein has particle size (D₅₀) ofpreferably 1 to 20 μm, more preferably 5 to 15 μm, and most preferably 7to 12 μm. In an aspect, the particle size is no less than about 5 μm,preferably no less than about 7 μm, and no more than about 15 μm,preferably no more than about 12 μm.

In an embodiment, the coating composition described herein includespolymeric filler material in an amount of preferably 0.1 to 10 parts perhundred (phr), more preferably 0.5 to 7 phr of the finished film weightof the coating.

In an embodiment, the coating composition described herein includes atleast one organic filler and at least one inorganic filler. Suitableinorganic fillers include, for example, pigment particles, mineralfillers, metallic materials, and the like. The inorganic filler ispreferably a mineral filler, more preferably an untreated amorphousmineral filler. Examples of suitable mineral fillers include, withoutlimitation, kaolin, talc, silica, mica, wollastonite, alumino-silicatematerial, and the like, and mixtures or combinations thereof. In apreferred aspect, the mineral filler is untreated amorphous silica.

The inorganic filler material described herein has (D₅₀) particle sizeof about 1 to 20 μm, preferably 5 to 15 μm, more preferably 10 to 14 μm.In an aspect, the particle size is no less than about 5 μm, preferablyno less than about 10 μm, and no more than about 15 μm, preferably nomore than about 14 μm.

In a preferred aspect, the coating composition described herein includesinorganic filler material in an amount of up to about 15 wt %,preferably about 1.5 to 10 wt %, based on the total weight of resinsolids in the composition.

The total amount of solids present in the coating composition describedherein may vary depending upon a variety of factors including, forexample, the desired method of application. For coil coatingapplications, the coating composition will typically include from about30 to about 65 wt % of solids. In some embodiments, the coatingcomposition may include as much as 80 wt % or more of solids.

Preferred cured coating compositions of the invention have excellentadhesion, hardness, flexibility, and demonstrate high tolerance todamage, especially during shipping, handling and installation. Thecombined properties of a smooth appearance and a damage-tolerant surfaceprovide a significant advantage over existing thermoplastic coatings,especially coil coatings.

The coating composition described herein may be applied by a variety ofmethods known to those of skill in the art. In an embodiment, thecomposition is applied to planar metal surfaces using a coil coatingprocess. The coating is preferably applied as a thin film, withthickness in the range of preferably 0.1 to 5 mil, more preferably 0.5to 2 mil, and even more preferably about 1 to 1.2 mil.

The coating composition has utility in a multitude of applications. Thecoating composition of the invention may be applied, for example, as anintermediate coat, as a topcoat, or any combination thereof. The coatingcomposition may be applied to sheet metal such as is used for externalbuilding wall panels, interior wall panels, architectural metal skins(e.g., gutter stock, window blinds, siding and window frames, etc.) andthe like, by spraying, dipping, or brushing, but is particularly suitedfor a coil coating operation where the composition is applied onto thesheet as it unwinds from a coil and then baked as the sheet travelstoward an uptake coil winder. It is further contemplated that thecoating composition of the invention may have utility in a variety ofother end uses, including, industrial coating applications such as,e.g., appliance coatings; packaging coating applications; interior orexterior steel building products; HVAC applications; agricultural metalproducts; wood coatings; etc. In a preferred aspect, the cured coatingdescribed herein is used as an exterior coating for building materials,architectural skins and the like.

Non-limiting examples of metal substrates that may benefit from having acoating composition of the invention applied on a surface thereofinclude hot-rolled steel, cold-rolled steel, hot-dip galvanized,electro-galvanized, aluminum, tin plate, various grades of stainlesssteel, and aluminum-zinc alloy coated sheet steel (e.g., GALVALUME sheetsteel).

The coating is typically cured or hardened in a heated temperatureenvironment of from about 200 to 500° C., more preferably from about 270to 470° C. For coil coating operations, the coating is typically bakedfor 8 to 25 seconds, to a peak metal temperature (PMT) of from about 200to 250° C.

EXAMPLES

The present invention is illustrated by the following examples. It is tobe understood that the particular examples, materials, amounts, andprocedures are to be interpreted broadly in accordance with the scopeand spirit of the invention as set forth herein. Unless otherwiseindicated, all parts and percentages are by weight and all molecularweights are weight average molecular weight. Unless otherwise specified,all chemicals used are commercially available from, for example,Sigma-Aldrich, St. Louis, Mo.

Example 1: Preparation of Coating Compositions

Coating compositions (#1 through #6) as shown in Table 1 were preparedby combining a binder system including PVDF and a curing agent. Thebinder and curing agent were blended together using standard mixingtechniques known in the art, along with different filler materials asshown in Table 1. The coating compositions were applied to metal panelsusing standard application methods, and baked at peak metal temperaturesof about 200° to 250° C. to provide coated test panels. The panels weretested for damage tolerance by measuring the number of cycles during alinear reciprocator test where the pressure applied to the coating wassimilar to the pressure used during typical forming operations. Resultsare shown in FIG. 1, where the highest damage tolerance corresponds tothe maximum cycles of failure at a low coefficient of friction.

TABLE 1 Coating Compositions Organic Inorganic filler Inorganic fillerCoating filler (>15 μm) (<15 μm) 1 (control) − + − 2 (inventive) + − + 3− − + 4 + + − 5 + − − 6 + − −

Having thus described the preferred embodiments of the presentinvention, those of skill in the art will readily appreciate that theteachings found herein may be applied to yet other embodiments withinthe scope of the claims hereto attached. The complete disclosure of allpatents, patent documents, and publications are incorporated herein byreference as if individually incorporated.

What is claimed is:
 1. A coated article, comprising a substrate; acoating disposed on thereon, the coating derived from a compositioncomprising: a binder component comprising at least a fluoropolymer; anorganic filler material having a particle size of no more than about 15μm; and an inorganic filler material having a particle size of no morethan about 15 μm wherein the coated article demonstrates increaseddamage tolerance relative to an article coated with a conventional coilcoating composition, and wherein the coated article demonstrates asmooth appearance.
 2. The coated article of claim 1, wherein thefluoropolymer comprises about 50 to 70% by weight of the resincomponent, based on the total weight of the composition.
 3. The coatedarticle of claim 1, wherein the fluoropolymer comprises up to about 70%by weight polyvinylidene difluoride (PVDF).
 4. The coated article ofclaim 1, wherein the resin component further comprises a polymer derivedfrom one or more ethylenically unsaturated monomers.
 5. The article ofclaim 1, wherein the coating comprises 0.5 to 7 phr of the organicfiller of finished film weight.
 6. The article of claim 1, wherein theorganic filler is a high molecular weight, high melting polyolefinmaterial.
 7. The article of claim 1, wherein the organic filler is apolyethylene.
 8. The article of claim 7, wherein the polyolefin materialis polytetrafluoroethylene (PTFE).
 9. The article of claim 1, whereinthe organic filler material has particle size of about 7 to 12 μm. 10.The article of claim 1, wherein the inorganic filler material is silica.11. The article of claim 1, wherein the inorganic filler material isuntreated amorphous synthetic silica.
 12. The article of claim 1,wherein the inorganic filler material has particle size of about 10 to14 μm.
 13. The article of claim 1, further comprising at least onecolored pigment.
 14. A coating composition comprising: a resin componentincluding at least one fluoropolymer; an organic filler material havinga particle size of no more than about 15 μm; and an inorganic fillermaterial having a particle size of no more than about 15 μm.
 15. Amethod of making a damage-tolerant coating, comprising: providing asubstrate; providing a coating composition, the composition comprising:a resin component including at least one fluoropolymer; an organicfiller material having a particle size of no more than about 15 μm; andan in 15 μm of no more than about 15 μm; applying the coatingcomposition on the substrate; and curing the applied composition toproduce a damage-tolerant coating.
 16. The method of claim 15, whereinthe substrate is a planar metal substrate.